Robert Downey Jr. won’t let his “Due Date” co-star, Zach Galifianakis, live down his role in the decision to drop Mel Gibson from “The Hangover 2.” Page Six first reported two weeks ago that troubled Gibson was tapped to play a tattoo artist in the sequel, but was dumped after other cast members complained. Introducing the Cinema Society’s “Due Date” screening Monday night, Downey teased, “Do you want to make any other big mistakes? Cost more people their jobs?” A speechless Galifianakis glared at him and walked off the stage after snatching Downey’s popcorn. At the after-party at Lavo, the Strokes’ Albert Hammond Jr. stepped out with Aussie model Nicole Trunfio, rumored to be his new love since his split with Agyness Deyn. Also at the DKNY Jeans-sponsored party: Darren Aronofsky, Rob Thomas, John Mayer, Courtney Love, Russell Simmons, Jamie-Lynn Sigler, Maria Sharapova and Jessica White.